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Questions tagged [speed-of-light]

The speed of light is a fundamental universal constant that marks the maximum speed at which energy and information can propagate. Its value is $299792458\frac{\mathrm{m}}{\mathrm{s}}$.

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Are cause and effect the same as in our Universe in a non-relativistic, Newtonian Universe in which the speed of light is infinite? [on hold]

Suppose the Universe was non-relativistic so time and space would be independent of each other. In other words, both of them separately would be absolute and independent of an observer's motion (...
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Energy of light

If a beam of light is travelling in full vacuum in same medium ,then , the energy of the light beam will decrease or not while moving through space ? The wavelength of the beam of light will change ...
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change frequency of monochromatic light without altering source?

When light goes from one medium to another its wavelength and velocity change while frequenccy remains the same. Also $E=h\nu$ ie.Frequency depends on energy, Now, given a light beam of given ...
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What would the effects be on the world if light slowed down? [duplicate]

It would be really helpful if the effects were just given in a list form so I can research them. The reason why I am asking this is because I to write an essay regarding the effects of a change in a ...
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Is it possible relativity could have been discovered much earlier? [closed]

Special relativity is a creation of Einstein. Mathematically unlike general relativity it is elementary. Is it conceivable Newton missed it? Or is it the case that it had to wait till the $20$th ...
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Light propagating through a sound wave

We know that the speed of light depends on the density of the medium it is travelling through. It travels faster through less dense media and slower through more dense media. When we produce sound, a ...
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It is said that an object cannot exceed the speed of light, because high speed makes the object closer to infinite mass, but speed relative to what?

That is, the speed of an object, when getting closer to speed of light, makes the mass of the object closer to infinite, but isn’t speed relative? So a man on earth feels a metal ball on the table has ...
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Will the log of wood sink in the water?

Imagine the water in a river is flowing with speed very close to the speed of light. There is a log of wood tied to any object outside the river so that it doesn't go ahead with water and is at rest ...
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How does a single photon behave propagating through glass?

Take a normal pane of window glass and a photon somewhere within the visible range. My limited understanding is that when light passes through glass one shouldn't think of little spheres travelling ...
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Applying information content limit to simulated universes [closed]

In simulated universe hypothetical scenario. It is often just considered that parent universes can simulate child universes, and those child universes can simulate further on etc... Yet, it seems ...
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How is reflection of light possible at all? [duplicate]

If a photon cannot be accelerated or decelerated, how is reflecting them possible at all?
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How to derive $c=1/\sqrt{\varepsilon_0\,\mu_0}$ from integral form of Maxwell equations? [closed]

I've read similar questions and answers given thereto but find them unsatisfactory. So please don't mark my question as "duplicate". The question may as well be a duplicate, but it's still waiting for ...
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Can we consider speed of light as escape velocity? [closed]

Consider following hypothetical scenario: A space ship starts to accelerate from planet Earth towards Alpha Centaury at a very pleasant 9,8m/s2.The astronauts onboard the ship keeps the acceleration ...
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Escape velocity of Kerr black Hole [duplicate]

Do the event horizon of Kerr black Hole have escape velocity is equal to the speed of light same Schwarzschild black hole?
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Recordings of journey traveling near speed of light

If you had two identical video cameras and started recording synchronized atomic clocks recording at the same speed and you put one on the spaceship and sent it out traveling at 99% of the speed of ...
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The hypotenuse of the triangle in the Michelson and Morley experiment

In Michelson and Morley experiment, light is travelling from light source to partially silvered glass plate. The plate splits an incoming beam of light, and the two resulting beams continue in ...
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Speed that a galaxy-sized newton's cradle would propagate motion

This doesn't necessarily have to be a newton's cradle, but the important point is that the length of the chain of spheres is exceptionally large (on the order of light years). Ignoring the effects of ...
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How do we get a expression for speed of light $\frac{1}{\sqrt{\mu\epsilon}}$ using Maxwell's equation? [duplicate]

I am a $12^{th}$ class student in India. I am quite new to these interesting concepts. And, I think I've learnt about electrostatics, magnetism, Maxwell's equations very thoroughly. But, my books ...
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How can someone calculate distance between Earth and Moon using a laser?

I have a book stating: When astronauts of the Apollo missions visited the moon, they placed a mirror on its surface, facing the earth. Then scientists on the earth sent a strong laser beam, which ...
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Role of motion in experimental results

This page contains:"If you are in a closed room on a ship sailing at a constant speed and the ride is perfectly smooth...[t]here’s no physical experiment you could conduct to tell whether you’re ...
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How does every ray of light or photon can follow the same Snell's law in a very random states of matter like gases and liquids?

We know that to study refraction at the interface of two media, we use Snell's law which is $$μ=\frac{\sin(i)}{\sin(r)}$$ or $$μ=c/v$$ (for vacuum as one of the media). I know this is an ...
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Relativity and Momentum of photons

I read somewhere that as the speed of a particle approaches c, its mass tends to infinity. Light is composed of particles (photons). If that is the case, then why don't we feel an enormous weight ...
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What exactly does the observer's coordinate system mean in special relativity?

This seems like a very basic question but I'm having a hard time understanding it, more precisely hard time visualizing it. Let say there is an observer, and we wish to somewhat formalize his ...
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Why didn't Lorentz conclude that no object can go faster than light?

Based on Lorentz factor $\gamma = \frac{1}{\sqrt {1-\frac{v^2}{c^2}}}$ it is easy to see $v < c$ since otherwise $\gamma$ would be either undefined or a complex number, which is non-physical. Also, ...
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What would happen if a planet's escape velocity exceeded the speed of light?

What would happen if a planet's escape velocity exceeded the speed of light? Would it also collapse into a black hole (by Heisenberg's uncertainty principle and Pauli's exclusion principle) or would ...
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Photon speed is it the same as light speed? [closed]

The speed of light is about 186000miles per sec. however, the light is also a wave. If the photon follows the wave path, then to progress at 186000miles / sec. in a linear direction must be ...
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Traveling to another galaxy impossible for ever?

If galaxies are moving apart from each other faster than the speed of light, does that mean that it's impossible to travel to another galaxy, regardless of what technology get discovered? Because you ...
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“flowing” speed of an electric field?

Consider a capacitor made of two infinite plates which are at a very large distance $d$ from each other. We place a positive charge on a plate and a negative one on the other one. Two electrical ...
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Is it possible to slow down the speed of light in a vaccum? [duplicate]

Is it possible to slow down the speed of light in a vaccum?
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Orientation of moving time clocks

Let's assume there's a high speed spaceship moving right relative to us, and it's carrying two light clocks. One of them is set up so that the bouncing light pulse is oriented horizontally, and in the ...
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1answer
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Can light in a medium travel faster than speed of light $c$ in vacuum?

Refractive index of medium $m$, $n_m$, is given by $$n_m = \sqrt{\mu_r\epsilon_r}$$where $\mu_r$ and $\epsilon_r$ are permittivity and permeability of the medium respectively. And, velocity of light ...
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What is Cherenkov radiation? [duplicate]

What is Cherenkov radiation? I came across this concept when I was learning SR. Why can't particles moving at speed of excess of speed of light in the medium. Why it does not violate the limitation ...
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Speed of waves in vacuum

All electromagnetic waves travel at speed of light in vacuum. Gravitional waves also travel at speed of light. I am having this vague notion that all waves in vacuum must travel at speed of light. Is ...
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Why is a particle non-relativistic when its kinetic energy is small compared to its rest energy?

For example, nucleons in nucleus are in motion with kinetic energies of 10 MeV. Their rest energies are about 1000 MeV. Kinetic energy of nucleons is small compared to rest energy. They are hence ...
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The Speed of Light and Its Medium's Density

When reviewing a refractive index chart there is a relationship to the density of the medium and the velocity of electromagnetic radiation through the medium. The lower the density the greater the ...
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Derivation of speed of light using particle theory

The speed of light can be calculated by Maxwell's equations, which tell us that light is an electromagnetic wave. How does the particle theory of light account for the constant speed of light?
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Speed of electromagnetic wave [closed]

On dispersion , speed of wave is inversely proportional to its wavelength . Therefore, gamma has max speed. But then in visible light , violet has least wavelength still it has least speed in visible ...
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Does gravity sometimes get transmitted faster than the speed of light?

Consider Earth moving around the Sun. Is the force of gravity exerted by Earth onto the Sun directed towards the point where Earth is "right now", or towards the point where Earth was 8 minutes ago (...
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If some matter slows light going through it, is actual causality also slowed? [duplicate]

tldr; If some forms of matter change the that light travels through that it (like refraction in water or glass), does that mean the speed of causality is going slower through that matter? I've heard ...
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Velocity of a photon according to a stationary observer in Schwarzschild metric

Consider the Schwarzschild metric $$ \left(1-\frac{2M}{r}\right)dt^2-\left(1-\frac{2M}{r}\right)^{-1}dr^2-r^2\left(d\theta^2+\sin^2\theta\, d\phi^2\right)$$ Final goal: calculate the observed ...
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Does space expansion mean the escape velocity at a black hole event horizon is strictly less than $c$?

The title pretty much sums it up. I could ask this question slightly differently; does the expansion of space cause the effective event horizon to shrink below what it would be for flat space? If so,...
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Turning on headlights near light speed [duplicate]

If i turn headlights on in a car at v = 0.99*c, will the headlight speed be 0.01*c? I know speed of light is always the same but it really confuses me? My question is, does space contract so much at ...
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speed of freezing vs. moving [closed]

An idea came to my mind and like to discuss it. We know that out there in the space the absolute zero (aka. -273 C) is almost reached where all the particles and atoms would freeze up and stop giving ...
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Rest mass of the photon [closed]

Why is the rest mass of the photon is taken to be zero? If rest mass of the photon is non zero, then it leads to infinite energy of the photon (by $E=mc^2$ equation) and there is a violation of ...
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Can we differentiate Einstein mass-energy relation $E=mc^2$ with respect to position $x$ to get force?

The question is as the title. Can we differentiate Einstein mass-energy relation $E=mc^2$ with respect to position $x$ to get force? I don't know whether my question is valid and logical but just ...
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Method to observe clocks on spaceships moving near $c$?

I have read the explanation for clocks slowing down on a spaceship moving relative to a stationary observer -- something like a beam of light between two mirrors taking longer for the observer to ...
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1answer
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How quickly is momentum transferred through an object? [duplicate]

If there was a pole, that was a light year long, out in space. (Away from all physical interference.) If we pushed one end of it, would the other end move instantly? And does it's speed depend on ...
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Can we measure the speed of light in one direction?

I'm sorry if this is a dumb question. Recently I was learning that it's impossible for us to measure the speed of light in one direction. We can only measure it in two directions and we assume that it'...
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Are tachyons time travelers?

If tachyons are faster than light, that means they have passed a certain point before anyone or anything can “see” them. Theories have mentioned that if anything can go faster than light, then it can ...
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Cooling photons to a solid state

Can we cool photons so the stop moving completely? So they can behave like particles in a solid.